The invention relates generally to optical networks. More particularly, the invention relates to an optical cross-connect switch for routing optical signals.
Optical networks generally achieve higher data rates and exhibit lower losses than their electronic counterparts. Optical cross-connect switches are often used to route optical signals between optical channels in the network. The cross-connect switches enable dynamic network requirements and improve network reliability. Some cross-connect switches utilize micro-electro-mechanical systems (MEMS) or related technologies and include an array of micro-mirrors. Each micro-mirror directs an incident input optical signal, or beam, to one of a group of output optical channels. The cross-connect switch typically includes a second mirror array to receive the reflected optical signals from a first mirror array and direct them to their respective optical channels.
In all-optical networks, it is generally desirable that the optical loss of each component be minimized. For the optical cross-connect switch, many factors contribute to the overall optical loss. Some loss contributors are functions of various parameters of the input optical signal. In particular, the polarization state of the input optical signal generally affects the optical power loss through the cross-connect switch. For example, the optical loss associated with reflection from each micro-mirror is a function of the beam angle of incidence at each mirror and the polarization state of the beam. Similarly, the optical loss associated with transmission through optical windows in the cross-connect switch is a function of the beam angle of incidence at each window and the polarization state of the beam. The variation in the output optical power represented for all possible polarization states of the input optical signal is defined as the polarization dependent loss (PDL) of the switch. It is generally desirable to reduce the PDL in order to reduce the variations in output optical power for the different switch channels or to avoid imposition of polarization control of the input beams.
The performance of optical networks is determined by the performance achieved by each of its components. Thus there remains a need for an optical cross-connect switch having reduced PDL.
In one aspect, the invention features an optical cross-connect switch having a first mirror array and a second mirror array. The first mirror array and second mirror array have mirror distributions defining a first array plane and a second array plane, respectively. The first mirror array is configured to receive an array of optical beam that are parallel to a first optical axis and to reflect the array of optical beams substantially parallel to a second optical axis. The second mirror array is positioned to receive the array of optical beams after reflection from the first mirror array. The first array plane defines a pair of axes orthogonal to each of the first optical axis and the second optical axis. One of the pair of axes is parallel to the first array plane and the other is parallel to the second array plane.
In another aspect, the invention features an optical cross-connect switch having a first fold mirror, a second fold mirror and a first mirror array. The first fold mirror has a surface and is configured to receive an array of optical beams that are substantially parallel to a first optical axis and to reflect the array of optical beams substantially parallel to a second optical axis. The first fold mirror defines a pair of axes orthogonal to the first optical axis and the second optical axis. The second fold mirror has a surface and is in optical communication with the first fold mirror. The second fold mirror is configured to receive the array of optical beams from the first fold mirror and to reflect the array of optical beams substantially parallel to a third axis. One of the pair of axes defined by the first fold mirror is parallel to the surface of the first fold mirror and the other of the pair of axes is parallel to the surface of the second fold mirror. The first mirror array is in optical communication with one of the first fold mirror and the second fold mirror along one of the first optical axis and the third optical axis, respectively.
In yet another aspect, the invention features a method of reducing polarization dependent loss in an optical device. The method includes reflecting a plurality of optical beams with a first mirror array to generate a plurality of reflected optical beams substantially parallel to a first optical axis. The first mirror array has an array surface and each of the reflected optical beams has a first polarization component that is parallel to the array surface of the first mirror array and a second polarization component that is orthogonal to the first polarization component. The reflected optical beams are reflected with a second mirror array which has an array surface that is parallel to the second polarization component.
In yet another aspect, the invention features an optical cross-connect switch having a first mirror array configured to receive and reflect an array of optical beams in a first average plane of incidence. The switch also has a second mirror array in optical communication with the first mirror array and configured to receive and reflect the reflected array of optical beams in a second average plane of incidence that is perpendicular to the first average plane of incidence.